单项选择题
The （） is a measure of the phase difference between voltage and current and is expected as the cosine of phase angle.
A.power B.efficiency C.effective power D.power factor
单项选择题 The overcurrent relay （） the motor contactor when the motor exceeds its rated current.
单项选择题 In a modern three-phase A-Csynchronous brushless generator, the excitation winding is on the rotorThat means （）.
单项选择题 Ammeter is to measure the （）.
